Heretofore, as an element capable of controlling the micro displacement of the order of sub-microns, a piezoelectric/electrostrictive element has been known. Particularly, in the piezoelectric/electrostrictive element, a piezoelectric/electrostrictive portion constituted of a piezoelectric/electrostrictive ceramic composition (hereinafter referred to simply as the “piezoelectric ceramic material”) and an electrode portion to which a voltage is applied are laminated on a base body constituted of a ceramic material. The element is suitable for the control of the micro displacement, and has excellent characteristics such as high electromechanical conversion efficiency, high speed response, high durability and saving of power consumption. The piezoelectric/electrostrictive element can be applied to various applications such as a piezoelectric pressure sensor, a probe movement mechanism of a scanning tunnel microscope, a rectilinear propagation guide mechanism in an ultra-precise processing device, a servo valve for hydraulic pressure control, a head of a VTR device, pixels constituting a flat panel type image display device and a head of an ink jet printer.
Moreover, the composition of the piezoelectric ceramic material constituting the piezoelectric/electrostrictive portion has variously been investigated. In recent years, an influence on a global environment, for example, the elution of lead (Pb) due to acid rain tends to be regarded as a problem. Therefore, as a piezoelectric/electrostrictive material in which the influence on the environment is taken into consideration, there has been developed an (LiNaK)(NbTa)O3-based piezoelectric ceramic material capable of providing a piezoelectric body or a piezoelectric element having satisfactory piezoelectric/electrostrictive characteristics without containing any lead (Pb).
The piezoelectric ceramic material is a ferroelectric body and is usually subjected to the polarization treatment to utilize the properties (the piezoelectric characteristics) thereof by incorporating the material in an electronic device or the like. This polarization treatment is a treatment in which a high voltage is applied so as to align the direction of spontaneous polarization in a specific direction, and the treatment is performed by applying the voltage to the piezoelectric ceramic material on appropriate temperature conditions. That is, in the ferroelectric body, a plurality of domains are present owing to charge deviation by the spontaneous polarization, and the piezoelectric ceramic material is subjected to the polarization treatment for aligning the directions of the ferroelectric domains in a predetermined direction, before used.
In addition, a piezoelectric material (the ferroelectric material) is a domain aggregate, and the domains are divided into a 180° domain and a non-180° domain. The 180° domain little contributes to strain, and the non-180° domain noticeably contributes to the strain. This is because the non-180° domain involves the rotation of the domain and hence the volume change of the domain increases. Moreover, during the above polarization treatment, the rotation of the non-180° domain occurs to generate a large strain.
However, the rotation of the non-180° domain, particularly a 90° domain indicating a large volume change has strong irreversibility. Therefore, once the polarization treatment for holding the material at a high voltage is performed, the strain decreases as compared with the strain generated during the polarization treatment. To solve the problem, there has been disclosed a piezoelectric material which produces a huge electrostrictive effect, when the reversibility of the domain rotation is intensified (Document 1: JP-A-2004-363557).
However, according to a manufacturing method of Document 1, an aging treatment requires days (five days to three months). Thus, the method is an inefficient method which incurs the increase of manufacturing cost.